Who among you have never experienced a flat bicycle tire from a thorny seed? Or tracked these same burrs in on the soles of your shoes? Or had to extract them from the paws of your dog? Well, my friend, you have had a close encounter with a puncturevine weed. So all together say -- arghhh!!
The puncturevine, Tribulus terrestris, is a member of the plant family, zygophyllaceae, also known as the caltrap family. Another member of this family is the creosotebush, a dominant native plant species of desert areas. Caltrap is Latin for foot trap. Caltraps were antipersonnel weapons used against advancing armies, especially in ancient times when horses, camels and elephants were used for soldier transportation. These weapons consisted of two or more sharp spines arranged so that one or more spines pointed upward. These could be used to slow the advance of armies and their vehicles.
The fruit of a puncturevine looks very much like a caltrap weapon! These are actually seed capsules that break into five sections, each containing 2-4 seeds. The puncturevine plant is a prostrate, mat forming weed with trailing stems up to five feet long. This annual weed has yellow flowers.
Puncturevine is a nonnative introduction from southern Europe. It can be found in gardens, pastures, waste areas and disturbed areas. This weed grows in dry climate areas and establishes especially along edges of roads. When road crews mow roadway borders, puncturevine spiny capsules get thrown out onto the road where it can then be quite hazardous to cycling.
Control is not that difficult if you follow a few rules. It is an annual weed and as such a pre-emerge herbicide containing trifuralin (Preen®, Treflan®) can be quite effective. But since seeds of this weed can lay dormant for 4-5 years, control is not usually accomplished in a single year.
Post emergent herbicides include Trimec®, Quadmec®, Triamine®, 2,4-D and glysophate (Roundup®). Trimec® and Quadmec® provide the best control, 95-100 percent of existing plants. Since dicamba is often in the mix of these post emergent herbicides, you must not treat areas that are within the dripline of trees and shrubs. If the dicamba leaches into the root zone of these non-target plants, significant damage can occur.
Cultural control consists of digging up the plants, being careful not to drop any of the spiny burrs. Better yet, dig up or spray these weeds before they flower, preventing further seed production. There is biological control available through the Palisade Insectary. I listed the seed and stem weevils in my previous column on this facility.
Until next time, enjoy what remains of our warm fall. Winter is just around the corner.
Jim Leser retired to Cedaredge in 2007 after a career with Texas A&M University Extension in entomology. He is a member of the Cedaredge Tree Board and a Colorado Master Gardener.